JPH05195467A - Method for improving selectivity of delignification of chemical paper pulp - Google Patents

Abstract

PURPOSE: To improve the selectively of delignification of a chemical paper pulp by treating unbleached pulp obtained by cooking operation with a solution of an organic peroxy acid under a specific condition. CONSTITUTION: An unbleached pulp obtained by cooking operation is treated in order to improve selectivity of delignification of a chemical paper pulp by an organic peroxy acid with an aqueous solution of the organic peroxy acid at 2-47 deg.C or preferably at 35-45 deg.C. Further the organic peroxy acid is preferably an aliphatic peroxy carboxylic acid having one percarboxy group and a saturated alkyle chain of less than 11C.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for delignification of chemical paper pulp. The invention particularly relates to methods for improving the selectivity of such delignification procedures.

[0002]

BACKGROUND OF THE INVENTION Unbleached chemical paper pulp obtained by cooking cellulosic material in the presence of chemical reagents is treated with a sequence of delignification and bleaching processes involving the use of oxidizer chemicals. It is known to process by. The purpose of this first step of the conventional continuous process for bleaching chemical pulp is to complete the delignification of the unbleached pulp, although delignification occurs after the cooking operation. This first delignification step conventionally reacts with residual lignin in the pulp by treating the unbleached pulp with chlorine in an acidic medium, or a mixed or continuous chlorine / chlorine dioxide combination. The chlorolignin may be extracted from the pulp in a subsequent processing step by solubilization of these chlorolignins in an alkaline medium. For a variety of reasons, it is clear that this first delignification step can be replaced in some situations by a treatment method that no longer uses chlorinating reagents. The treatment of chemical pulp with a first step at a temperature of about 50 ° C. and pH values of 3 to 9 involving peracetic acid has already been proposed (Bail
ey CW and Dence CW, "Peroxyacetic Acid Bleaching
of Chemical Pulps ", Tappi, January 1966, Volume 49, N
o.1, pages 9-15). However, in this known method, this peracetic acid treatment results in a pulp having inferior viscosity and mechanical properties to pulp delignified by conventional processes involving chlorine in an acidic medium.
It is evident as a result of the lower selectivity of delignification which appears in the more pronounced attack of the cellulose chains.

[0003]

The object of the present invention is to achieve an efficient delignification of unbleached chemical pulp with a high selectivity, which makes it possible to obtain a pulp with a high degree of original quality. By providing a method, the drawbacks of known methods are eliminated.

[0004]

To this end, the present invention relates to a process for improving the selectivity of delignification of chemical paper pulp with organic peroxyacids, whereby unbleached pulp resulting from a cooking operation. Are treated with this aqueous solution of organic peroxyacid at a temperature of 2-47 ° C. According to the invention, chemical paper pulp refers to the presence of chemical reagents such as sodium sulphide (kraft or sulphate digestion) in alkaline medium, sulfur dioxide or metal sulphite (sulphite digestion) in acidic medium. It is understood to mean pulp which has been subjected to delignification treatment. Pulp where cooking is carried out using sulfite in a neutral medium (also known as neutral sulfite cooking, NSSC cooking), or alternatively treatment with caustic soda at low temperature, followed by machine Disaggregation (me
Semi-chemical pulps, such as those obtained by mechanical defibering, may also be bleached and / or delignified by the method of the present invention. The latter is directed, inter alia, to pulps which have undergone kraft cooking, whose residual lignin content after cooking depends on the type of wood species from which they originate and on the potency of the cooking process, kappa numbers between 8 and 40. ) (Or 5 to 3)
Has a potassium permanganate value of 0). All types of wood used for the production of chemical pulp are suitable for carrying out the process of the invention, especially those used for kraft pulp, i.e. for example pine of various species and Softwoods such as fir, and hardwoods such as eucalyptus, beech, oak and hornbeam.

According to the invention, the organic peroxyacid is 1
Selected from aliphatic peroxycarboxylic acids containing one percarboxylic group and a saturated linear or branched alkyl chain of less than 11 carbon atoms. Aliphatic peroxycarboxylic acids with saturated linear alkyl chains containing less than 6 carbon atoms are preferred. Examples of such peroxy acids are performic acid, peracetic acid, perpropionic acid, n-perbutanoic acid and n-perpentanoic acid. Peracetic acid is particularly preferred due to its potency and good biodegradable properties.

In a variant of the process according to the invention, the organic peroxyacid is substituted on a linear or branched alkyl chain having less than 16 carbon atoms and on each other carbon atoms located in the alpha and omega positions. Selected from diperoxycarboxylic acids containing two percarboxylic groups. Examples of such peroxyacids are 1,6-diperoxyhexanedioic acid, 1,8-diperoxyoctanedioic acid, 1,10-
These are diperoxydecanedioic acid and 1,12-diperoxidedecanedioic acid. In another variation of the method of the present invention, the organic peroxy acid is at least 1 per benzene ring.
Selected from aromatic peroxy acids containing one percarboxyl group. Preferably, aromatic peroxy acids containing one percarboxyl group per benzene ring are selected. An example of such an acid is peroxybenzoic acid.

Another variant of the process according to the invention consists in choosing organic peroxyacids which are substituted by one or more halogen atoms or any other functional organic substituent.
Any other functional organic substituent includes carbonyl groups (ketones, aldehydes or carboxylic acids), alcohol groups, nitrogen-containing groups such as nitriles, nitros, amines and amides, and sulfur such as sulfo and mercapto groups. It is understood that it means a functional group such as a containing group. The peroxy acid can be equally used in the state of an aqueous solution of peroxy acid or ammonium salt, alkali metal salt or alkaline earth metal salt of the peroxy acid.

Preferably, the treatment with organic peroxyacid is carried out at a temperature of 35 to 45 ° C. Generally, the treatment is carried out at atmospheric pressure with the organic peroxyacid. This treatment time depends on the temperature and the wood species used to produce the pulp and the previous digestion. About 12
Times from 0 minutes to about 240 minutes are highly preferred, and without risking a substantial loss of mechanical resistance of the pulp.
It is possible to exceed this limit even to about 100%. At higher processing temperatures, i.e. above 45 ° C, less time of about 45 minutes to about 120 minutes can be used. The treatment of the present invention can be carried out in any type of equipment suitable for treating paper pulp with acidic, neutral or alkaline reagents. The unbleached pulp storage room, which is present in all bleaching installations and serves as a buffer reservoir between the wood cooking unit and the pulp bleaching unit, is particularly suitable for carrying out the process of the invention. The pulp can therefore be processed therein during storage without the need for costly investment in special equipment. The possibility of safely exceeding the normal processing time is particularly well suited to the role of storage buffer in the storage compartment.

The consistency in the treatment step with organic peroxyacids is generally chosen to be 2-40% dry matter, usually 10-40%. A high consistency, for example 20-40% is preferred. In the process of the present invention, the amount of organic peroxy acid used is selected according to the level of residual lignin in the pulp and the average treatment time. Generally, for that dry pulp
Peroxy acids in amounts of 0.5-4% by weight are suitable. Most often, an amount of peroxyacid of not more than 3% by weight and more than 1% by weight, based on the dry pulp, is used.

As a variant, prior to the treatment with this organic peroxyacid, decontamination pretreatment with an aqueous acid solution (decontamina
It is advantageous to carry out a ting pretreatment process. The purpose of this step is to extract impurities from the pulp that are present in the form of metal ions that interfere with the successful progress of the bleaching and / or delignification operations. Suitable, alone or as a mixture, are all inorganic or organic acids used in aqueous solution. For example, strong inorganic acids such as sulfuric acid or hydrochloric acid are highly preferred. It is advantageous to carry out the acid decontamination pretreatment in the presence of a substance which forms a complex with a metal ion. For this purpose, mixtures of the abovementioned strong inorganic acids with organic acids of aminopolycarboxylic acids or aminopolyphosphonic acids or their alkali metal salts are highly preferred. Examples of suitable aminopolycarboxylic acids are diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid, cyclohexanediaminetetraacetic acid and nitrilotriacetic acid. Diethylenetriaminepentaacetic acid (DTPA) is preferred. Examples of aminopolyphosphonic acids are diethylenetriaminepentamethylenephosphonic acid (DTMPA), ethylenediaminetetra (methylenephosphonic) acid, cyclohexanediaminetetramethylenephosphonic acid (CDTMPA) and nitrilotri (methylenephosphonic) acid. DTMPA is preferred.

The operating conditions for this acid decontamination pretreatment are not critical. They should be determined in each particular case according to the type of paper pulp and the equipment in which the treatment is carried out. Generally speaking, the choice of acid and its amount to be used should be established to bring the pH of the medium to below 7, for example from about 1 to about 6.5. A particularly advantageous pH value is about 2.0.
Is about 5.0. Its temperature and pressure are not critical,
Room temperature and atmospheric pressure are generally highly preferred. The pretreatment time can vary within wide limits depending on the type of equipment used, the choice of acid, the temperature and the pressure, for example from about 15 minutes to
It's a few hours. It is also possible to replace this decontamination pretreatment by incorporating in the delignification step with peroxyacid itself one or more substances that form a complex with the metal ion. These complexing agents are selected from the same complexing agents as those suitable for the decontamination pretreatment step described above.

In another variant of the process of the invention, when it is desired to obtain a high level of whiteness, the treatment with peroxyacids is followed by conventional bleaching with or without chlorinating reagents. A series of steps can be continued. Examples of such steps are: steps using gaseous oxygen or ozone, steps using alkaline hydrogen peroxide in the presence or absence of gaseous oxygen, chlorine dioxide or the following: Process steps using sodium chlorite and alkali extraction with caustic soda. The following examples are given for the purpose of illustrating the invention and are not intended to limit the scope of the invention.

[0013]

EXAMPLES The measurements made in the examples which follow are carried out according to the following standard method. Copper Index: TAPPI Method T2
36, CM85. Viscosity: TAPPI Method T2
30, OM89. A sample of Ponderosa pine kraft pulp with a Kappa index of 28.4 and a viscosity of 32.1 mPs was subjected to a delignification step with an aqueous solution of peroxyacetic acid, followed by alkaline extraction in the presence of hydrogen peroxide (Paa E
p sequence). Four tests were carried out, two under the conditions of temperature and time of the prior art (designated as comparative examples 1 and 2) and 2 under the conditions of the invention (designated as examples 1 and 2). Will be done). Comparative Example 1 did not include a water wash of the pulp between the peroxyacetic acid treatment step and the alkali extraction step as compared to the other three examples. The hydrogen peroxide present during the alkali extraction step of Comparative Example 1 is also derived from the residual hydrogen peroxide from the preceding peroxyacetic acid step. In Example 2, according to the present invention, the peroxyacetic acid step was performed after acid pretreatment (step Q) with diethylenetriaminepentaacetic acid or DTPA. In each of these tests, 2.0 g of peroxyacetic acid was given per 100 g of dry pulp. The peroxyacetic acid used was an aqueous solution on the market, which contained hydrogen peroxide in equilibrium with the peroxyacetic acid (2.6 g H ₂ O ₂ for 100 g dry pulp). The working conditions and the results obtained are shown in the table below.

[0014]

[Table 1] Chemical Reagent% Time Temperature Kappa Viscosity Example Process PAA H ₂ O ₂ NaOH DTPA min ℃ Index Mps ─────────────────────────── ────────── Comparative Example 1 Paa 2.0 2.6 60 70 24.0 Ep 2.0 5.4 60 60 17.8 19.5 ──────────────────────── ──────────── Comparative example 2 Paa 2.0 2.6 60 70 24.0 Ep 0.5 3.0 60 75 16.5 19.4 ────────────────────── ────────────── Example 1 Paa 2.0 2.6 240 38 22.9 Ep 0.5 3.0 60 75 16.4 24.4 ──────────────────── ──────────────── Example 2 Q 0.3 15 45 Paa 2.0 2.6 120 45 25.3 Ep 0.5 2.0 60 75 15.2 29.3 ────────────── ──────────────────────

With respect to the unwashed pulp, the delignification and loss of viscosity after alkali extraction are as follows.

[0016]

[Table 2] Example Delignification (%) Loss of viscosity (%) ────────────────────────── Comparative Example 1 37.3 39.2 Comparative Example 2 41.9 39.6 Example 1 42.2 24.0 Example 2 46.5 8.7 ───────────────────────────

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.

Claims (10)

[Claims] 1. A method for improving the selectivity of delignification of a chemical paper pulp with an organic peroxy acid, the unbleached pulp obtained from a cooking operation being treated by the method with an aqueous solution of the organic peroxy acid. And the treatment is carried out at a temperature of 2-47 ° C. 2. The temperature of the organic peroxyacid treatment is 35 to 35.
Method according to claim 1, characterized in that it is at 45 ° C. 3. The organic peroxyacid is one selected from the group consisting of one percarboxylic group and an aliphatic peroxycarboxylic acid containing a saturated linear or branched alkyl chain having less than 11 carbon atoms. The method according to claim 1, characterized in that there is. 4. A linear or branched alkyl chain having less than 16 carbon atoms and two percarboxyl groups substituted on the carbon atoms located at the alpha and omega positions relative to each other. The method according to claim 1, which is one selected from the group consisting of diperoxycarboxylic acids containing 5. The organic peroxy acid is one selected from the group consisting of aromatic peroxy acids containing one percarboxyl group per benzene ring,
The method of claim 1. 6. Process according to claim 1, characterized in that the organic peroxyacid is used in the form of one of its ammonium, alkali metal or alkaline earth metal salts. 7. Process according to claim 1, characterized in that the process is carried out in a storage compartment for the unbleached pulp which is sent to a bleaching unit. 8. The method according to claim 1, wherein a step of decontamination pretreatment with an aqueous acid solution is performed before the treatment with the organic peroxy acid. 9. The method of claim 8, wherein the aqueous acid solution contains at least one compound that sequesters metal ions. 10. A compound for sequestering metal ions is used during the peroxyacid treatment.
The method of claim 1.